This invention relates in general to optical switches, and more specifically, to a conical fiberoptic switch.
With the advance of fiberoptic technology, information signals have been increasingly transmitted through optical fibers. Signal transmission through optical fibers has significant advantages over electrical transmission methods. Signals transmitted optically are not disturbed by electromagnetic noise. Use of optical fibers is advantageous in many environments where the use of metal electrical conductors is undesirable, such as in chemically active and corrosive environments.
As in electrical signal transmission, it is frequently necessary in optical signal transmission to change the transmission path of information signals by switches. In some applications, it is necessary to have the option of connecting one fiber with either one of two other fibers. In other applications, it may be necessary to exchange the connection between two input fibers and two output fibers. In still other applications, it may be necessary to select a connection between one fiber and a number of other fibers. Therefore, it is desirable to provide a wide variety of optical switches capable of performing different functions.
Two types of optic fibers have been used: multimode and single mode. While multimode fibers have good light-gathering ability, the wider diameter of the multimode fiber allows diverse internal zigzag paths which may cause mode dispersion. The mode dispersion caused limits the useful bandwidth transmitted. With narrower diameters than the multimode fibers, single-mode fibers can transmit very wide bandwidths. Multimode fibers, however, are less disturbed by misalignment than single-mode fibers. Therefore, while a misalignment of a few microns may cause negligible transmission loss in multimode fibers, the same misalignment may cause irretrievable information loss when single-mode fibers are used. Therefore, one common problem of conventional optical switches is misalignment of the fibers connected by the switches. It is therefore desirable to provide fiberoptic switches which can accurately align input and output fibers. It is also desirable to provide fiberoptic switches that are inexpensive and easy to use.
One conventional optical switch is described in U.S. Pat. Nos. 4,834,488 and 4,896,935. As shown in FIGS. 9 and 11 of these two patents, one conventional design envisions the use of a number of fixed fibers and one movable fiber which may be rotated to be in optical alignment with one of the fixed fibers. The movable fiber and the fixed fibers are all located in the same plane. In some applications, it may be cumbersome to have to rotate the movable fiber by large angles. This is particularly true where it is desirable to align, not just one movable fiber with one fixed fiber at a time, but to align a group of fibers with another group of fixed fibers amongst a number of groups of fixed fibers at one time.
Another type of fiberoptic switch is disclosed in U.S. Pat. No. 4,378,144 to Duck et al. Duck et al. discloses an optical switch in which a number of output fibers is arranged parallel to the axis of a stepping motor and around a pitch circle centered at the axis of the motor. An input fiber is rotated about the axis of the stepping motor to be at one of a number of switching positions along the pitch circle so as to be aligned with one of the output fibers. The above-described design by Duck et al. is disadvantageous for many reasons. Since the output fibers are arranged parallel to the axis of the stepping motor and surround the stepping motor and since the input fiber is rotated along the circumference of the pitch circle to be aligned with the output fibers, Duck et al.'s device occupies considerable space and may be impractical for switching applications requiring a physically small device. Furthermore, in such an arrangement, the diameter of rotation of the input fiber by the stepping motor becomes a limiting factor in regard to the accuracy of alignment. Since the input fiber is spaced apart from the axis of the motor at a distance that must be at least as great as the radius of the stepping motor, any variations in angular displacement of the stepping motor will cause significant alignment errors.
In view of the reasons above, it is desirable to provide an improved optical switch in which the above-described difficulties are alleviated.